As the sage puppets from Avenue Q pointed out, we’re all a little bit racist. Everyone from out-and-proud bigots to social justice activists have preconceived notions because, psychologically speaking, biases are firmly ingrained perspectives that people unknowingly acquire and carry through life.

Sleep may hold the key to shedding these unconscious biases.

A team of psychologists from Northwestern University, lead by cognitive scientist Ken Paller, conducted a series of studies on reactivating memories during sleep. In short, they’ve figured out how to manipulate what information we remember by playing different sounds while we’re sleeping. In the most recent study, published on May 28in Science, Paller and his team found they could use the technique to weaken people’s race and gender biases.

The Study

Participants took tests designed to assess two implicit biases. The first test gauged their associations between female faces and words related to art and science. The second gauged their associations between black faces and positive/negative words. As researchers expected, participants subconsciously adhered to stereotypes of women as non-scientific and people of color as bad or violent.

Next, participants performed a Pavlovian-esque brain-training task designed to reverse their biases. They watched face-word pairings flash across a screen and were told only to respond to those that contradicted stereotypes: female faces with science words and black faces with good words. When they responded correctly, they heard distinct sounds for each type of pairing.

After the brain training, participants took the implicit bias tests again and, across the board, exhibited less bias toward both female and black faces.

Then, they napped. Once they entered deep sleep (or Slow Wave Sleep), researchers replayed one of the two sounds from the training. Each participant heard either the sound associated with female faces and science words or black faces and good words.

Post-nap, they took the implicit bias tests again. This time, researchers saw further reductions in bias only for the type of face that corresponded to the sound played during participants’ naps. In other words, subjects who heard the women-science sound exhibited even less bias toward female faces, but showed no change in their level of bias towards black faces. And vice versa.

A week later, during the fourth and final round of implicit bias testing, participants’ reduced bias toward the type of face (female or black) associated with the sound they heard during their naps remained unchanged. But, their biases toward the other type of face increased. Reinforcing the bias training during sleep seemed to have a long-lasting effect on reversing subconscious prejudice.

Why would sleep be so critical to this process, given how difficult it is to overcome bias consciously? Sleep, specifically the Slow Wave Sleep phase, is critical to memory consolidation, which is the process of converting new information into long-term memories. By playing sounds associated with specific information — or in the case of bias training, newly acquired perspectives — scientists seem able to manipulate which perspectives stuck and which didn’t.

It may not be entirely our fault that we unconsciously harbor biases based on certain social characteristics. But, that doesn’t mean we shouldn’t lessen our prejudice if we can. As plenty of research has shown, implicit biases inform our decisions and treatment of other people. If sleep memory reactivation is as powerful as the Northwestern team’s ongoing research suggests, perhaps our ingrained biases will become something we choose to overcome rather than accept as inevitable.